title: Computed gray levels in multislice and cone-beam computed tomography.
abstract: BACKGROUND
  Gray level is the range of shades of gray in the pixels, representing the x-ray attenuation coefficient that allows for tissue density assessments in computed tomography (CT). An in-vitro study was performed to investigate the relationship between computed gray levels in 3 cone-beam CT (CBCT) scanners and 1 multislice spiral CT device using 5 software programs.
  
  
  METHODS
  Six materials (air, water, wax, acrylic, plaster, and gutta-percha) were scanned with the CBCT and CT scanners, and the computed gray levels for each material at predetermined points were measured with OsiriX Medical Imaging software (Geneva, Switzerland), OnDemand3D (CyberMed International, Seoul, Korea), E-Film (Merge Healthcare, Milwaukee, Wis), Dolphin Imaging (Dolphin Imaging & Management Solutions, Chatsworth, Calif), and InVivo Dental Software (Anatomage, San Jose, Calif). The repeatability of these measurements was calculated with intraclass correlation coefficients, and the gray levels were averaged to represent each material. Repeated analysis of variance tests were used to assess the differences in gray levels among scanners and materials.
  
  
  RESULTS
  There were no differences in mean gray levels with the different software programs. There were significant differences in gray levels between scanners for each material evaluated (P <0.001).
  
  
  CONCLUSIONS
  The software programs were reliable and had no influence on the CT and CBCT gray level measurements. However, the gray levels might have discrepancies when different CT and CBCT scanners are used. Therefore, caution is essential when interpreting or evaluating CBCT images because of the significant differences in gray levels between different CBCT scanners, and between CBCT and CT values.
authors.affiliation: Department of Orthodontics, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, RS, Brazil.
authors.forename: Fabiane
authors.initials: F
authors.lastname: Azeredo
authors.forename: Luciane Macedo
authors.initials: LM
authors.lastname: de Menezes
authors.forename: Reyes
authors.initials: R
authors.lastname: Enciso
authors.forename: Andre
authors.initials: A
authors.lastname: Weissheimer
authors.forename: Rogério Belle
authors.initials: RB
authors.lastname: de Oliveira
mesh_terms: D000388:Air; D000465:Algorithms; D002133:Calcium Sulfate; D003116:Color; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation* / Q000592:standards; D006171:Gutta-Percha; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D061330:Multidetector Computed Tomography / Q000295:instrumentation* / Q000592:standards; D019904:Polymethyl Methacrylate; D012015:Reference Standards; D015203:Reproducibility of Results; D012984:Software; D036542:Tomography, Spiral Computed; D014867:Water; D014885:Waxes
chemical_list: D014885:Waxes; D014867:Water; D006171:Gutta-Percha; D019904:Polymethyl Methacrylate; D002133:Calcium Sulfate